1. Field of the Invention
The present invention relates to an improvement in a structure of an electric switch.
The present invention especially concerns a structural improvement in an electric switch of push-on type wherein the switch turns to an on-state when its actuator is being pushed towards a moving contact member of the switch.
2. Description of the Prior Art
In conventional electric switches of the push-on type, there has been a problem that undesirable dust is likely to be introduced into a space between the moving contact and the fixed contact. Such problem in the conventional switch is elucidated referring to FIG. 1 which is a sectional elevation view of one example of such known push-on type switch, wherein a plastic case 1 contains in its recess 11 a central fixed contact 2a at center, a pair of other fixed contacts 2b,2b at apart position from the center, a known partial-hemisphere-face-shaped resilient metal diaphragm disk 3 as a moving contact disposed spanning and contacting the pair of fixed contacts 2b,2b with its periphery and a plastic pushing member 4 overriding the moving contact 3. A lid 5 is placed on the case 1 to prevent the pushing member 4 from going out of the case 1. Lead-out terminal tabs 2a' and 2b' are connected to the fixed contacts 2a and 2b, respectively. When the pushing member 4 is pushed down, a protrusion 4b provided underneath thereof pushes the central part of the moving contact 3 as shown by a white arrow A in FIG. 2(b), the moving contact quickly changes its form from a normal state shown in FIG. 2(a) into a partially inversed strained state of FIG. 2(b), and the central part of the diaphragm-shaped moving contact 3 touches the central fixed contact 2a. When the pushing force to the pushing member 4 is removed, then the moving contacts restores to initial normal state as shown by FIG. 2(c), thereby pushing up the pushing member 4 as shown by a white arrow B.
When the diaphragm-shaped moving contact 3 quickly changes its shape from the normal state of FIG. 2(a) to the strained state of FIG. 2(b), air in the space covered by the moving contact 3 is pushed out as shown by arrows x,x in FIG. 2(b), and when the moving contact 3 restores from the strained state of FIG. 2(b) to the normal state of FIG. 2(c), air is sucked into the space under the moving contact 3 as shown by arrows y,y in FIG. 2(c). When the air is sucked into the space, dust in the recess 11 of the case is brought into the space and on the central fixed contact 2a. Such dust is then pressed on the surfaces of the fixed contact or the moving contact by contacting of fairly smooth flat faces thereof. Therefore, the dust is likely to stay there and thereby becomes an obstacle against good contact.